A sequence cassette encoding the GAL4(DBD)::Zip- hemidriver followed by transcription stop sequence has been inserted into the endogenous fru locus, resulting in the endogenous fru P1 promoter driving expression of GAL4(DBD)::Zip- instead of the fru[M] isoform, while expression of fru transcripts from the P2-P4 promoters can still occur.